The present invention relates to silicone release coating compositions and inhibitors therefor. More particularly, the present invention relates to a blend of a dialkyl carboxylic ester having carbon to carbon unsaturation and an olefinic carboxylic acid ester of an aliphatic alcohol as an inhibitor for precious metal catalyzed polysiloxane compositions which are particularly well suited for solventless silicone release coating compositions.
Silicone compositions have long been used for rendering surfaces nonadherent to materials which would normally adhere thereto. For a long time it was necessary that these silicone coatings be applied as a dispersion within a solvent in order to control the viscosity of the coating material so as to be suitable for coating applications. However, although the solvent aids in the application of the coating, it is a highly inefficient process inasmuch as the solvent must thereafter be evaporated. The evaporation of solvents requires large expenditures of energy and, additionally, pollution control requirements mandate that solvent vapors be prevented from escaping into the environment. Thus, removal and recovery of solvents entails considerable expenditures for apparatus and energy.
Consequently, solventless release coating compositions, sometimes referred to as 100% solids release compositions, have been developed. The absence of a solvent in such compositions both lowers the amount of energy required to effect curing and eliminates the need for expensive pollution control equipment. However, a problem associated with such silicone release coatings relating to premature gelation must be overcome. Since a typical composition is made up of a vinyl chain-stopped base polymer, a cross-linking agent and a platinum metal catalyst, premature curing or gelation may occur in a short period of time, thus resulting in a product with an unsatisfactory pot-life. When the composition is ready for use it is desirable that the catalyzed polymer composition have a sufficiently long pot-life to enable the end-user to carry out the coating application. Accordingly, the coating composition is provided with an inhibitor which effectively retards the hydrosilation addition cure reaction of the composition at ambient temperature, but does not retard the cure at elevated temperatures. Examples of inhibitors which have been utilized in prior art solventless release compositions include vinyl acetate, diallylmaleate and triallylisocyanurate (TAIC).
Eckberg in U.S. Pat. No. 4,256,870 discloses a silicone composition comprising a base polymer such as a vinyl chain-stopped polydialkyl-alkylvinyl polysiloxane base copolymer and a methylhydrogen cross-linking fluid. This composition is catalyzed by platinum or a platinum metal complex which will initiate an addition cure reaction. An inhibitor selected from organic esters of maleic acid is added to the composition in order to selectively retard the cure reaction so as to provide a workable pot-life for the coating composition.
Eckberg in U.S. Pat. No. 4,262,107 discloses a silicone rubber composition with good pot-life and fast curing at elevated temperatures comprising a silanol end-stopped diorganopolysiloxane polymer, a silicone hydride cross-linker and a rhodium complex catalyst in combination with an inhibitor compound selected from low molecular weight silanol end-stopped diorganopolysiloxane, certain acetylenic compounds, olefinic carboxylic acid esters of aliphatic alcohols such as vinyl acetate, alkenyl isocyanurates and mixtures of such inhibitor compounds.
Eckberg in U.S. Pat. No. 4,347,346 discloses a solventless platinum or rhodium catalyzed addition curable polyorganosiloxane release coating composition containing a dialkylacetylenedicarboxylate inhibitor for preventing premature gelation at ambient temperatures but which still cure at elevated temperature via a hydrosilation reaction to form a coating capable of releasing materials from substrates which would normally adhere thereto.
A novel multi-component solventless silicone release system is disclosed by Grenoble and Eckberg in Ser. No. 458,421, filed Jan. 17, 1983, assigned to the same assignee as the present invention, and which is incorporated herein by reference. Therein it is disclosed that prior art two-component systems, one part of which comprises a vinyl silicone fluid, precious metal catalyst and an inhibitor, and the other part a polymethylhydrogensiloxane crosslinker, unduly limit the flexibility of the end-user to formulate solvent-free silicone release coatings which more precisely meet their performance and cost requirements. Accordingly, there is provided a multi-component system wherein the ingredients are provided the end-user in three or more separate parts to provide such flexibility. While such a multi-component system substantially eliminates the problem of premature gelation over an extended period of time, it is also desirable to further increase the useful pot-life of release coating compositions to extend the period of time during which the end-user can carry out the coating application.
Thus, there is provided by the present invention a solventless silicone release coating composition containing a two-part inhibitor which not only exhibits more effective inhibition than similar concentrations of the individual ingredients, but also improves the solubility of such inhibitor in silicone fluids. Hence the present invention provides a significant improvement over prior art release coating compositions containing a one-part inhibitor.
It is therefore a primary object of the present invention to provide a solventless composition which will render surfaces non-adherent to materials which would normally adhere thereto.
Another object of the present invention is to provide a solventless coating composition which will cure to a coating having satisfactory smear, rub-off, migration and release characteristics.
A further object of the present invention is to provide a solventless coating composition which has a satisfactory pot-life or bath-life in its catalyzed form when it is ready for use.
Still another object of the present invention is to provide a method of rendering materials nonadherent to other materials which would normally adhere thereto.
It is still a further object of the present invention to provide a release coating composition having a two-part inhibitor which effectively retards the catalyzed cross-linking reaction at temperatures below the heat cure temperature of these compositions and to provide solventless silicone compositions which are particularly well suited for paper release applications.
These and other objects will become apparent to those skilled in the art upon consideration of the present description, examples and claims.